Preparation of silicon-fluoride silicones

ABSTRACT

A method is disclosed of selectively displacing hydride with fluoride at chain silicon positions in organopolysiloxane compounds. Also, 3-fluoroheptamethyltrisiloxane and the polymeric fluoro derivatives of liquid silicone hydrides are disclosed which have high thermal stability properties and are useful as high temperature-resistant release coatings.

United States Patent Britt et al.

[54] PREPARATION OF SILICON-FLUORIDE SILICONES [72] Inventors: A. D. Britt, Falls Church, Va.; William B.

Moniz, Clinton, Md.

73 Assignee: The United States of America as represented by the Secretary of the Navy 22 Filed: July 27,1970

21 Appl.No.: 58,737

[52] U.S. Cl ..260/46.5 R, 117/1 39.5 A, 117/142, 252/49.6, 260/465 H, 260/4482 R, 260/4482 E [51 Int. Cl. ..C08f 1 1/04 [58] Field of Search ..260/46.5 H, 46.5 R, 448.2 E, 260/4482 R [56] References Cited UNITED STATES PATENTS 2,981,746 4/1961 Cohen et al ..260/448.2 3,198,766 8/l965 Nitzsche et a]. ..260/46.5

FOREIGN PATENTS OR APPLICATIONS 627,800 8/1949 Great Britain ..260/46.5

[451 May 23, 1972 OTHER PUBLICATIONS Britt et al., Hydride-Fluoride Conversions in Organosiloxane Chains, 3-Fluoroheptamethyltrisiloxane, Journal of the American Chemical Society, 91, 6204- 6205, October 22, 1969.

Simons, Fluorine Chemistry, Vol 1, pp. 32- 33, I950, Academic Press, NY.

Primary ExaminerD0nald E. Czaja Assistant Examiner-M. I. Marquis Attorney-R. S. Sciascia, Arthur L. Branning and James G. Murray ABSTRACT A method is disclosed of selectively displacing hydride with fluoride at chain silicon positions in organopolysiloxane compounds. Also, 3-fluoroheptamethyltrisiloxane and the polymeric fluoro derivatives of liquid silicone hydrides are disclosed which have high thermal stability properties and are useful as high temperature-resistant release coatings.

3 Claims, No Drawings PREPARATION OF SILICON-FLUORIDE SILICONES STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION icones and, with very few exceptions, possess carbon-fluorine rather than silicone-fluorine bonds. Silicon-fluorine bonds occur at terminal positions in structures such as the disiloxanes, the silyl ethers, and the siloxy esters of boron.

Chain silicon-fluorine bonds are known in octafluorotrisiloxane (F SiOSiF OSiF and in two trifunctional compounds, (SiO, ,,F), and fluorotris(triphenylsiloxy)siloxa ne. The first compound is not a silicone and both trifunctional compounds are solids. For true silicone fluids, two patents disclose chain silicon-fluorine bonds, Brit. Pat. No. 627,800 and U.S. Pat. No. 2,981,746. Unlike the present invention which directly converts an extant silicone fluid into a chain siliconfluorine silicone fluid, both patents employ the customary hydrolysis synthesis using non-silicone starting materials. Also, both the British and U.S. patents utilize an acid environment in which to carry out their synthesis. However, pmr observations and infrared measurements disclose that chain silicon-fluorine bonds in liquid silicones will be destroyed under even dilute HP or HCI acid environments. Under such conditions, the fluoride will migrate to carbon forming a C--F bond and leaving behind a Si-I-I bond. Consequently, the formulas assigned to the organofluorosiloxane polymers disclosed in the British and U.S. patents are in fact inaccurate.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided the conversion of an extant silicone fluid possessing silicone hydride chain units into chain units of silicone-fluorine. The terminal chain groups and all other original structural features are unaffected. The synthesis, isolation and characterization of 3-fluoroheptamethyltrisiloxane is also disclosed.

STATEMENT OF THE OBJECT OF THE INVENTION It is an object of this invention to provide novel polyorganofluorosiloxane fluids having silicon-fluorine linkages at one or more chain silicon positions.

It is a further object of this invention to provide a novel method for the preparation of polyorganofluorosiloxane fluids having silicon-fluorine linkages at one or more chain silicon positions.

A still further object of this invention is to provide a method for the preparation of polyorganofluorosiloxane fluids having silicon-fluorine linkages at one or more chain silicon positions that is selective, quantitative, and without appreciable side reactions.

Another object of this invention is to provide a method for the preparation of polyorganofluorosiloxane fluids having silicon-fluorine linkages at one or more chain silicon positions that utilizes existing silicone fluids.

It is an additional object of this invention to synthesize, isolate and characterize a linear organofluorosiloxane molecule bearing a (-RSiF) unit.

Still other objects, features and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this invention, polyorganosilicone fluids which may contain a single silicone hydride group or repeating chain silicone hydride groups and having the formula wherein R, to R, comprises an alkyl selected from the group consisting of methyl, ethyl, and propyl radicals and n is an integer from 1 to approximately 40 are reacted with silver fluoride to produce a polyorganofluorosiloxane fluid containing one or more chain silicone fluoride groups and having the wherein R, to R, comprises an alkyl selected from the group consisting of methyl, ethyl, and propyl radicals and n is an integer from 1 to approximately 40. The R, to R, alkyl groups of the fluid are not affected or altered by the selective reaction with silver fluoride.

The reaction may be carried out with equimolar quantities of silicone hydride and silver fluoride, but a slight molar excess of the fluoride is usually desired to ensure high yields. When chain silicone hydride precursors are used, i.e. when n is greater than one, it is difficult to isolate and specifically characterize the structure formed. Comparative NMR analyses show, however, that chain hydride substituents are converted to fluoride along the chain and that the remainder of the polymer remains the same.

One of the preferred silicone hydrides useful in this invention is rnethylhydrogenpolysiloxane. This commercially available hydride contains repeating units of the formula and is readily available from various commercial sources.

A specific example of a preferred methylhydrogenpolysiloxane is DC 1 107. Infrared spectrum analysis, refractive index, and elemental composition data indicate that DC 1 107 has the following structure EXAMPLE I Dissolve one gram of 3hydrido-heptamethyltrisiloxane in ml acetone. Add one gram silver fluoride in small increments of a few milligrams at a time over a period of 3 to 4 hours at 25 C. A vigorous reaction occurs at the solid silver fluoride liquid interface. The reaction product had the following formula as determined by proton NMR analysis and the yield exceeded 90 percent.

EXAMPLE ll Wash 1.5 grams silver fluoride with 5-10 ml portions of acetone until the wash liquid tests neutral to litmus. Store the washed silver fluoride under benzene and use within 24 hours. Dissolve one ml of 3-hydrido-heptamethyltrisiloxane in a ml solution of 50 percent benzene and 50 percent acetone.

Add the purified silver fluoride, a few milligrams at a time,

until substantially no more hydrogen gas is evolved; this normally takes 3-4 hours at ambient conditions. The reaction mixture may be agitated to facilitate escape of H gas, however, too vigorous of a reaction or warming of the mixture is to be avoided due to the volatility of the 3-hydride precursor. After the reaction is completed, the mixture is centrifuged, filtered and then purified by gas-liquid chromatography. The product was 3-fluoroheptamethyltrisiloxane in yields above 95 percent. It was a colorless volatile liquid having a boiling point of 148 C. at 754.5 mm Hg. Refractive index was 1.3704 measured at 25 C. Elemental analysis gave:

fluorine 7.81% 7.90%

The volatility of the product affected the which was in sealed gelution capsules.

C-H analysis but not the F analysis EXAMPLE ll! Dissolve 1.6 gm DC 1107 in a l0 ml solution of 50 percent benzene and 50 percent acetone. Use the same procedure and conditions delineated in example II to obtain the fluorinated derivative product. NMR analysis showed retention of the main features of DC 1 107 but with a hydride decrease and a new shoulder on the downfield side of the chain CH resonance doublet, indicating formation of a [CH SiFl moiety. The product was a clear silicon-fluorine bonded silicone which, in thermal stability tests, was infusible at 400 C.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by letters patent of the U.S. is:

1. A process for preparing a silicon-fluoride bonded silicone composition comprising reacting equimolar quantities of silver fluoride and a silicone hydride having the formula 1%. Li J. i.

where R to R-, are alkyls selected from the group consisting of methyl, ethyl, and propyl radicals and n is an integer from I to approximately 40.

2. The process of claim 1 wherein a slight molar access of silver fluoride is used.

3. The process of claim 1 wherein the reaction is continued until substantially no hydrogen gas is evolved. 

2. The process of claim 1 wherein a slight molar access of silver fluoride is used.
 3. The process of claim 1 wherein the reaction is continued until substantially no hydrogen gas is evolved. 